Soundproofing is generally divided into two categories: one is absorbing sounds, and the other is insulating sounds. Mainly, styrofoam, sponge, cork, paper egg tray, etc. has been used for sound absorption and polymers such as a concrete has been used for sound insulation.
Referring to a principle of the sound absorption, the sound absorption is divided into two sub-categories. One is a principle of absorbing sounds with a certain material, and for example porous materials such as sponge, cork, etc. may be sued to absorb sounds. On the while, and the other is a principle of using vibration of membrane of a board or a fabric to absorb sounds.
However, the above conventional sound absorbers have many problems. For example, soundproof materials made of wood or plastic resin are vulnerable to fire due to their fragility to heat, and glass fiber, rock wool, etc. not only become the cause of environmental pollution due to floating dust, but also generate toxic gases when a fire breaks out.
Also, there was developed a soundproof panel with a perforated structure wherein a perforated thin panel is attached to a surface of a material such as glass fiber, rock wool, plastic resin, etc., but the soundproof panel is difficult to solve intrinsic defects presented by glass fiber, plastic resin, etc., and also its manufacturing process is very complex and requires much costs upon its construction.